There has been a remarkable vindication over the past 15 years of Burnet’s forecast, with two particular themes of dominant interest to research on immunogenetics. The first is the association in inbred animals between genetic control of immune responses to antigens of limited heterogeneity and genes (Ir genes) of the major histocompatibility complex (MHC) [2, 39]. The second is the increasing refinement of typing methods for human histocompatibility antigens, of relevance to tissue transplantation, and associations between certain immunopathic diseases and HLA specificities [26, 31]. However, despite much experimental work and theoretical speculation, no unifying concept relating MHC-linked Ir genes effects and MHC- linked disease susceptibility has yet emerged.